Gap tube motor

ABSTRACT

The gap tube motor comprises a rotor, a stator and a gap tube which is arranged between the rotor and the stator, with at least two bearing apparatuses being arranged with a spacing in the axial direction (A) with respect to the rotor, and with at least one of the bearing apparatuses being designed as a bearing and drive apparatus and comprising both an electrical motor drive apparatus and a magnetic bearing apparatus in order to both drive the rotor and to journal the rotor in the radial direction without contact using this bearing and drive apparatus.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a gap tube motor including a gap tube arrangedbetween a rotor and stator.

2. Description of the Prior Art

In pumps, for example, for aggressive liquids or for water of highestpurity, a complete separation between the drive motor and the pump isrequired. It is known to use a gap tube motor or canned motor, which hasa gap tube arranged between the stator and the rotor, for applicationsof this kind. It is known to suspend the rotor of a gap tube motorhydrostatically or by means of a sliding bearing. A gap tube motorhaving a sliding bearing has, for example, the disadvantage thatabrasive substances contained in the liquid can already destroy thesliding bearing after a short operating period. In addition, the liquidcan be contaminated by the particles of the sliding bearing. A gap tubemotor having a hydrostatic bearing has, for example, poor dry runningproperties. Moreover, liquids with volatile substances, i.e. liquidswith gas components, can be forwarded only poorly.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an economically moreadvantageous gap tube motor.

This object is satisfied by a gap tube motor in accordance with thefeatures of claim 1. The subordinate claims 2 to 8 relate to furtheradvantageous embodiments of the invention.

The object is satisfied, in particular, in that the gap tube motorcomprises a rotor, a stator and a gap tube which is arranged between therotor and the stator; in that at least two bearing apparatuses arearranged at a spacing in an axial direction with respect to the rotor;and in that at least one of the bearing apparatuses is formed as abearing and drive apparatus and comprises both an electric motor driveapparatus and a magnetic bearing apparatus in order to both drive therotor and to journal it in the radial direction without contact usingthis bearing and drive apparatus.

In an advantageous embodiment of the gap tube motor, the latter isconnected to a forwarding apparatus for a fluid, in particular to acentrifugal pump. In a further advantageous embodiment, the rotor of thegap tube motor is magnetically journalled without contact by at leasttwo magnetic bearing apparatuses which are arranged with a spacing inthe axial direction. In a further advantageous embodiment, the onemagnetic bearing apparatus of the gap tube motor is designed as abearing and drive apparatus comprising an electric motor drive apparatusand a magnetic bearing apparatus. In a particularly advantageousembodiment, the bearing and drive apparatus of the gap tube motor isdesigned as a bearing-less motor with a motor winding which is arrangedin the stator and a control winding which is arranged in the stator,with the motor winding having a number of pole pairs p and the controlwinding having a number of pole pairs p±1.

An advantage of the gap tube motor in accordance with the invention isto be seen in the fact that the rotor can be designed with purelypassively operating components and in that the coils which magneticallyjournal or magnetically drive the rotor are arranged so that they areseparated from the rotor by a gap tube. The rotor is therebymagnetically journalled without contact and the space surrounding therotor is hermetically separated by the gap tube with respect to thestator. In this way a gap tube pump can be manufactured having a rotorwhich is journalled without contact and in which the space surroundingthe rotor is hermetically separated from the stator by the gap tube.Through this hermetic separation, the gap tube pump in accordance withthe invention is suitable, in particular, for the forwarding ofsubstances of high purity such as water or enzymes of biochemicalprocesses. Abrasive substances containing chemicals can also beforwarded using the gap tube pump in accordance with the invention,since the rotor is journalled without contact and thus the abrasivesubstances can not damage the bearing apparatus. The gap tube pump inaccordance with the invention has excellent dry running properties sincethe rotor is magnetically journalled without contact even in the absenceof a fluid or in the presence of strongly gassing or highly volatilefluids.

The invention will be explained with reference to a plurality ofexemplary embodiments. Shown are:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 2 is a longitudinal section through an exemplary embodiment of agap tube motor with a centrifugal pump;

FIG. 3 is a longitudinal section through an exemplary embodiment withsymmetrically arranged gap tube motors and with a centrifugal pump lyingtherebetween;

FIG. 1a is a cross-section through FIG. 3 along the line A--A;

FIGS. 4, 5, 6, 7 show a longitudinal section through a further exemplaryembodiment of a gap tube motor with a centrifugal pump;

FIG. 8 is an exemplary embodiment of a magnetic radial bearing designedas a unipolar bearing;

FIG. 9 is a gap tube motor with an excitation apparatus.

DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

FIG. 2 shows a gap tube motor 1 which is designed with an outer rotor 3and is connected to a centrifugal pump 2 via a shaft 9c. The centrifugalpump 2 sucks in a fluid flowing in the direction 24a via the inletopening 20 and forwards it by means of a rotating impeller or rotorwheel 22 flowing in the direction 24a to the outlet 21. The gap tubemotor 1 and the centrifugal pump 2 have a common axis of rotation A. Thestator 4 of the gap tube motor 1 is arranged to lie inwardly and has acore 4a of a magnetically conducting material, in particular of iron, atthe surface of which iron lamina of sheet iron 11 are arranged, whichextend in the radial direction and into which electrical conductors 12are embedded in the manner which is usual in electric motors. All ironlamina 11 together form a laminated stator pack. The electricalconductors 12 are arranged in such a manner that an electromagneticrotary field can be produced in order to set the outwardly disposedrotor 3 in rotation. The stator 4 has a cylindrical cut-out 4c thereception of a track bearing 10. The centrifugal pump 2 produces a forcewhich acts in the flow direction 24a during operation and which istransmitted via the shaft 9c, 9a and the track bearing 10 to the stator4. The stator 4 is surrounded by a hollow cylindrical rotor 3 which isdesigned as an external rotor and which is designed as an outer rotorand which has permanent magnets 8 arranged on the axially extendinginner surface near the stator 4. The rotor 3 can also be designed insuch a manner that an induction or a reluctance motor results togetherwith the stator 4. At the end near the centrifugal pump 2, the hollowcylindrical rotor 3 has a disc-shaped terminal part 3b which isconnected to the shaft 9c in order to drive the impeller 22. The rotor 3can, in addition, have a hollow cylindrical connection 9d which connectsthe disc-shaped terminal part 3b to the centrifugal pump 2, with theconnection part 9d having a diameter corresponding to the outer diameterof the rotor 3 in the exemplary embodiment illustrated in FIG. 2.

The gap tube motor 1 and the centrifugal pump 2 are surrounded by acommon pressure-resistant housing 5. The gap tube motor 1 has a gap tube18 in which at least the surface of the stator 4 or the lamella 11facing the rotor 3 is or are surrounded by a means 18 which isimpermeable to fluid or liquid or is or are surrounded by a gap tube 18respectively. This gap tube 18 can consist, in particular, of a metal,of a metal alloy such as Hastelloy C22, or of a plastic, in particular,of a corrosion resistant material.

The gap tube motor pump 1, 2 formed in this manner has an opening 23 fora liquid passage so that the liquid first flows in the axial direction7a between the rotor 3 and the housing 5 starting from the high pressurepart of the pump 2, then flows back in the opposite, axial direction 7bbetween the rotor 3 and the stator 4 and in so doing forms ahydrodynamic radial bearing for the rotor 3. The liquid flows furthertowards the axis of rotation A, passing in a radial direction to theaxis of rotation A between the stator 4 and the disc 3b, whereupon ahydrodynamic axial bearing for the rotor 3 forms between the end facesof the stator 4 and the oppositely disposed surface of the disc 3b. Theliquid flows via an opening 9b into the shaft 9c and further through thehollow shaft 9c to the inlet 20 of the centrifugal pump 2. The shaft 9chas an extension part 9a which is journalled in the cylindrical cut-out4c of the stator 4 by a track bearing 10. The track bearing 10 isrequired, in particular, for starting up the centrifugal pump 2, whereasduring the forwarding operation the hydrodynamic axial bearing formedbetween the stator 4 and the disc 3b suffices in order to compensate theforces acting in the axial direction.

The disc-shaped terminal part 3b can also be connected to the shaft 9a,9c without an aperture 9b. The gaps 6a, 6b are thereby filled withliquid, but a flow direction 7a, 7b arises, however, in the axialdirection A. Thus, the rotor 3 has a hydrodynamic bearing acting, inparticular, in the radial direction.

The rotor 3 can be equipped as illustrated with permanent magnets 8 orcan be designed as a cage rotor or a reluctance rotor.

A stator 4 can have cavities, such as, for example, at the electricalconductors 12, in the end region of the stator 4. Cavities of this kindcan be filled with a filler such as a casting resin or with an oil sothat the liquid impermeable layer also lies on the filler.

An advantage of the gap tube motor 1 in accordance with the invention isto be seen in the fact that the layer 18 which is impermeable to liquidis arranged on the surface of the cylindrically designed stator 4. Sincethis layer 18 is subjected exclusively to a pressure loading, it can bemade very thin and/or consist of an elastic material such as a plastic.A further advantage of the gap tube motor 1 is to be seen in the factthat the liquid flowing in the gap 6a, 6b, 6c can have a very highpressure without damaging the layer 18 which is impermeable to liquid. Afurther advantage of the gap tube motor 1 is to be seen in the fact thatthe core 4a of the stator 4 can also be manufactured of a ceramic, sothat the stator 4 has a high pressure resistance and the track bearing10 has advantageous bearing properties.

The gap tube motor 1 has two bearing apparatuses 30a which are arrangedspaced apart in the direction of the axis A and are both designed as aso-called bearing-free motor. A bearing-free motor of this kind producesa torque on the rotor 3 in the drive direction as well as a force on therotor 3 in the radial direction in order to journal the rotor 3 withoutcontact. The stator 4 of a bearing-free motor of this kind has a winding12 with a number of pole pairs p for the production of the torque, andan additional control winding 12a for the contact-free journalling ofthe rotor 3, with the control winding 12a having a number of pole pairsp±1. Further sensors 15 with an integrated position sensor are arrangedin the stator 4 in order to measure the position of the rotor 3 relativeto the stator 4 and to pass it on to a control or regulating apparatus40. The stator 4 has passages 4b for the reception of electricalconductors 13 which are led to the windings 12, 12a and to the sensors15 starting from a distributor device 14. The signals of the sensors 15are received by a measuring apparatus 45 and fed to a control apparatus40 which correspondingly excites the windings 12 and the controlwindings 12, 12a via a setting apparatus or controller 41, 42, 43, 44and the distributor devices 14 which are placed after it.

An electronic control system 40 receives the values of the sensors 15and excites the control windings 12, 12a in such a manner that theposition of the rotor 3 is controlled in the radial and/or axialdirection in such a manner that the rotor 3 as well as the centrifugalpump 2 with the wheel 22 which is connected to it is magneticallyjournalled and can rotate freely. This kind of magnetic bearing isadvantageous, for example, for the starting up and running down of thecentrifugal pump 2 because the liquid has a relatively low pressure inthese operating states so that the liquid 7a, 7b flowing in the gap tube6a, 6b does not ensure that the rotor 3 and the stator 4 do not comeinto mutual contact. The actively regulated magnetic bearing prevents amutual contact between the rotor 3 and the stator 4, in particular,during a standstill of the motor, with an emergency running bearing 10or a track bearing 10 being provided in the case of larger arisingforces in order to transmit the forces acting to the stator 4. It canprove advantageous to arrange an active axial magnetic bearing at thestator 4. FIG. 2 shows an active magnet at the end face of thecylindrical stator 4, the active magnet being designed in the form of aring and having a ring winding 16 which is arranged in a terminal part16a of good magnetic conductivity. This active magnet with the ringwinding 16 enables the rotor 3 to be drawn towards the stator 4. Duringthis, the liquid located between the disc-shaped terminal part 16a ofthe stator 4 and the disc-shaped termination of the rotor 3 produces ahydrodynamic bearing with a force acting in the direction towards thecentrifugal pump 22. The active magnet with the ring winding 16 producesa force opposed to the former. The distance between the two terminalparts 3b, 16a is monitored by a sensor 15. This sensor signal is fed toa control apparatus 40 which excites the active magnet with the ringwinding 16 in accordance with the desired values.

FIG. 1a shows a cross-section through FIG. 3 along the line A--A. Thestator 4 has a plurality of cut-outs 4e or grooves 4e extending parallelto the axis A. In the cross-section of FIG. 1a the embedded electricalconductors 12 are illustrated in only a few grooves 4e in order tosimplify the illustration. In the assembled motor, however, all grooves4e have an embedded electrical conductor 12. The conductors 12 can bearranged and excited in such a manner that they can be operated with arotary current and that a rotary magnetic field thereby arises in thestator 4. The thin layer 18 which is impermeable to fluid or liquid,which is not illustrated in FIG. 3, i.e. the gap tube 18, can be seen inFIG. 1a. Going from the outside inward, the rotor 3 first has a layer 18which is impermeable to fluid or liquid, followed by a laminated rotorpack 3a, a layer of permanent magnets 8 polarized in the radialdirection and finally a layer 18 which is impermeable to fluid or liquidlying on the permanent magnets 8. For the permanent magnets 8, thedirection of the magnetization is indicated with arrows, with themagnetization extending in the radial direction and with individualpermanent magnets 8 being adjacently arranged in the peripheraldirection in such a manner that regions with magnetization pointingradially outwardly and regions with magnetization pointing radiallyinwardly arise. The laminated stator pack 11 and the grooves 4e arecovered over towards the gap 6b with a layer 18 which is impermeable tofluid or liquid so that the entire stator is protected against a liquidpresent in the gap 6b.

FIG. 3 shows a longitudinal section of a gap tube motor 1 with twosymmetrically arranged stators 4 and two rotors 3 connected via a commonshaft 9c. The centrifugal pump 2 is fastened to the common shaft 9c. Thecentrifugal pump 2 and the gap tube motors 1 are arranged in common in apressure resistant housing 5, 5a, 5b. A layer 18 which is impermeable toliquid is again arranged at the surface of the stator 4. Starting fromthe pressure side 24b, the gap flow flows between the housing 5 and therotor 3 passing in the axial direction 7a, flows further in the oppositedirection 7b between the rotor 3 and the stator 4, and opens into theshaft 9c via an aperture 9b. It then flows through the shaft 9c at itscenter passing in the axial direction, exits again at the motor 1 whichis arranged at the left via the opening 9b flowing between the rotor 3and the stator 4, and subsequently flows between the housing 5 and therotor 3 to the suction side 24a of the centrifugal pump 2. Ahydrodynamic bearing is thereby achieved. In the exemplary embodiment ofFIG. 3, the two electric motors 1 are designed as bearing-less motors,as described in FIG. 2. An advantage of the embodiment of FIG. 3 is tobe seen in that the symmetric arrangement of the motors 1 producessmaller bearing forces, in that the lever arm between the centrifugalpump 2 and the motor 1 turns out to be shorter, and in that it isthereby possible to operate a pump having a plurality of pressure stagesbetween the motors 1 in a simple manner.

FIG. 4 shows a further exemplary embodiment of a centrifugal pump 2driven by a gap tube motor 1. This gap tube motor 1 again has aninwardly lying stator 4 and an outwardly lying rotor 3. The gap tubemotor 1 again has a radial bearing formed by the fluid flows 7a, 7b anda hydrodynamic axial bearing produced by the fluid flows 7f flowing inthe radial direction, with the fluid flowing in a cut-out arranged inthe centre of the shaft 9c in the axial direction to the right into ahydraulic bearing apparatus 30c. The fluid flows back to the suctionside 24a of the centrifugal pump 2 in the direction 7d and 7e. Thehydraulic bearing apparatus 30c which is arranged on the right sidelikewise produces a journalling of the shaft 9c in the radial and in theaxial direction. In the exemplary embodiment of FIG. 4, the bearing anddrive apparatus 30a is again designed as a bearing-free motor.

FIG. 5 shows a further exemplary embodiment of a gap tube motor 1 whichhas an outwardly lying rotor 3. The stator 4 has a bearing and driveapparatus 30a on the left side which is designed as a bearing-free motorand a bearing apparatus 30b on the right side designed as an activelyregulated radial magnetic bearing 27. In addition, the stator has anactively regulated axial magnetic bearing 16, 16a. The sensors 15monitor the position of the rotor 3 relative to the stator 4. Thedisc-shaped termination 3b of the rotor 3 has a ring-shaped cut-out 26b.The stator 4 has a ring-shaped projecting part 26a disposed opposite tothis cut-out 26b. The two components 26a, 26b together form a passivemeans 26a, 26b for the regulation of the hydrodynamic bearing. Thepassive means 26a, 26b serve for the compensation of the position of therotor 3 with respect to the stator 4 in the axial direction.

FIG. 6 shows a further exemplary embodiment of a gap tube motor 1 withan inwardly lying rotor 3 which is surrounded by a gap tube 18 and by anoutwardly lying stator 4, 4a. The gap tube motor 1 has two bearingapparatuses 30a, 30b which are arranged spaced apart in the axialdirection and which hold the rotor 3 without contact in the stator 4, 4ain the radial direction through magnetically acting means. The onebearing apparatus 30a is designed as a bearing-free motor, the stator 4aof which has a motor winding 12 with a number of pole pairs p and acontrol winding 12a with a number of pole pairs p±1. In the rotor 3 ofthe bearing-free motor 30a, windings 12c which extend in the axialdirection are arranged in which an electric current is induced by themagnetic rotary field produced by the motor winding 12 and the controlwinding 12a. The winding 12c is designed as a short circuit winding. Theother bearing apparatus 30b is designed as a magnetic bearing with acontrol winding 12b. A control winding 12b of this kind usuallycomprises three or four separately excitable windings in order to beable to suspend the rotor 3 without contact. This magnetic bearing 30bis advantageously arranged as near to the vaned wheel 22 as possible inorder to keep the length of the part of the shaft 9a extending betweenthe magnetic bearing 30b and the vaned wheel 22 as short as possible, sothat this part of the shaft 9a forms only a short lever arm with respectto the forces produced by the vaned wheel 22 in the radial direction.The distance between the stator 4 and the rotor 3 amounts to 1 mm in theradial direction, with the gap tube 1 having a thickness of 0.6 mm andthe air gap a separation of 0.4 mm. The position of the rotor 3 ismonitored by sensors 15, with these sensors 15 being arranged to beseparated from the rotor 3 by the gap tube 18. An eddy current sensor,an inductive sensor or a Hall sensor with a permanent magnet is suitableas a measurement principle. An axial magnetic bearing apparatus 50 isarranged at the left end of the rotor 3. The one part of the bearingapparatus 50 is arranged inside the gap tube 18 and comprises amagnetically conducting body 35b which is designed in the shape of a uand extends circularly in the peripheral direction of the rotor 3 aswell as a permanent magnet 35c which is correspondingly arranged in thebody 35b in order to produce a permanent magnetic force which acts onthe disc 3b of the shaft 9a in the axial direction. The further part ofthe bearing apparatus 50 is arranged outside the gap tube 18 andcomprises a circularly extending magnetically conducting body 35a whichis designed in the shape of a u and has an excitable electrical coil 35which is arranged in the u-shaped cut-out. This coil 35 can be excitedby a control apparatus 41 so that the axial position of the rotor 3,which is monitored by a sensor 15a, can be influenced in a controlledmanner.

FIG. 7 shows an arrangement similar to the exemplary embodiment of FIG.6, with the rotating wheel 22 of the centrifugal pump 2 being arrangedbetween the bearing-free motor 30a and the magnetic bearing 30b. At theside of the inlet 20 the rotating wheel 22 has a hollow cylindricalextension 9d which is designed to be magnetically conducting andcooperates with the magnetic bearing 30b in such a manner that thisextension 9d is held without contact in the radial direction bymagnetically acting forces.

FIG. 8 shows an exemplary embodiment of a magnetic bearing apparatus 30bwhich holds a rotor 3 without contact in the radial direction by meansof magnetically acting forces. A magnetic bearing apparatus 30b designedin such a manner is termed a unipolar bearing and has two rotary fieldmachine stators 53, 54 each having three discretely formed coils 53a,53b, 53c; 54a, 54b, 54c. A permanent magnet 55 which is polarized in theaxial direction is arranged between the rotary field machine stators 53,54 and produces a unipolar flux flowing from the one rotary fieldmachine stator 53 to the rotor 3 and from the latter back again to therotary field machine stator 54. The coil pairs 53a, 54a; 53b, 54b; 53c,54c are preferably connected in series and are excited by a three-phaserotary current source in such a manner that the rotor 3 is journalled inthe magnetic bearing 30b without contact. In an advantageous embodiment,the rotor 3 has a groove 3z extending in the peripheral direction. Thisgroove 3z effects a stabilizing of the rotor 3 in the axial direction,that is, produces, in the event of a deflection of the rotor 3, amagnetic force in the axial direction opposite to the deflection. Amagnetic bearing 30b in accordance with embodiment illustrated in FIG. 8can, for example, be used in a gap tube motor 1 in accordance with FIG.6. The rotor 3 forms a part of the shaft 9a. If the magnetic bearing 30bhas a groove 3z, the part of the axial bearing 50 arranged inside thegap tube 18 can be dispensed with, since a bias force acting in theaxial direction can be produced through the relative arrangement of theshaft 9a and the magnetic bearing 30b in the axial direction.

Also suitable as a further embodiment of a magnetic bearing 30b, forexample, is a stator with three coil bodies which are designed in theshape of a "u", which are arranged with spacing in the peripheraldirection, and each of which has a controllable coil in order tomagnetically journal a rotor 3 without contact.

FIG. 9 shows an excitation apparatus in combination with a gap tube pumpin accordance with the embodiment illustrated in FIG. 6. The position ofthe rotor 3 is measured with a plurality of sensors 15 and supplied to asignal processing apparatus 45 via electrical lines 45a, 45b, 45c, 45dwhich transmits the position of the rotor to a higher level controlapparatus 40. This control or regulating apparatus 40, which usuallycomprises a computer, controls the axial bearing 50 via the converter41, the two coils 12 and 12a of the bearing-free motor 30a via theconverters 42 and 43, and the magnetic bearing 30b via the converter 44.The position of the rotor 3 can be controlled in the radial directionand in the axial direction by the illustrated control apparatus in sucha manner that the rotor 3 is journalled without contact in the stator 4.In addition, the control apparatus 40 controls the bearing-free motor30a, with which the rotor 3 is driven, via the two coils 12 and 12a.

The bearing and drive apparatus 32 can also be designed in such a mannerthat an electric motor 31 and a magnetic bearing apparatus 30b arecombined in such a manner that both an effect supporting the rotor 3 andan effect driving the rotor 3 arise. For example, the magnetic bearingapparatus 30b can be arranged immediately adjacent to the electric motor31. Suitable for a driving electric motor 31, for example, is asynchronous motor or a brushless DC motor with permanent magneticexcitation or with an excitation winding excited by a current. Likewisesuitable is an induction motor or a reluctance motor.

What is claimed is:
 1. A gap tube motor comprising a rotor, a stator anda gap tube which is arranged between the rotor and the stator wherein atleast two bearing apparatuses are arranged with a spacing in the axialdirection with respect to the rotor; and wherein at least one of thebearing apparatuses is designed as a bearing and drive apparatus andcomprises both an electrical motor drive apparatus and a magneticbearing apparatus in order to both drive a rotor and journal the rotorin the radial direction without contact through this bearing and driveapparatus; and wherein the bearing and drive apparatus is designed as abearing-less motor with a motor winding having a number of pole pairs parranged at the stator as well as a control winding having a number ofpole pairs p±1.
 2. A gap tube motor in accordance with claim 1 whereinthe bearing and drive apparatus comprises an electric motor and aseparately arranged magnetic bearing apparatus.
 3. A gap tube motor inaccordance with claim 1 wherein the rotor is designed as an inner rotoror as an outer rotor.
 4. A gap tube motor in accordance with claim 1wherein all bearing apparatuses are designed as magnetic bearingapparatuses for the contact-free journalling of the rotor in at leastthe radial direction.
 5. A gap tube motor in accordance with claim 1wherein at least one sensor is provided for the measurement of theposition of the rotor; wherein a gap tube is arranged between the sensorand the rotor; and wherein the sensor is based on a magnetic measurementprinciple and, in particulars is designed as an eddy current sensor, aninductive sensor or a Hall sensor.
 6. A gap tube motor in accordancewith claim 1 wherein an actively magnetizable coil for influencing theaxial position of the rotor is arranged in such a manner that the gaptube extends between the rotor and the coil.
 7. A gap tube motor inaccordance with claim 1 wherein the magnetic bearing apparatuses are fedby a three-phase rotary current controller.
 8. A gap tube pumpcomprising a forwarding means for a fluid, in particular a centrifugalpump, as well as a gap tube motor in accordance with claim
 1. 9. Anapparatus comprising a gap tube motor in accordance with claim 8.